The present invention relates to a self-correcting watch, and more particularly to an electronic watch having a circuit for correcting its time indication automatically.
FIG. 3 is a block diagram illustrating a self-correcting watch of the prior art (hereafter called the first prior art) disclosed in a Japanese patent application laid open as a Provisional Publication No. 170088/'90.
In the prior art of FIG. 3, a forward signal 47a or a late signal 47b having a certain pulse width according to a correction value, +3 sec or -5 sec, for example, is impressed to a polarity register 40, by manipulating a correction switch 31. The polarity register 40 registers a signal polarity, that is, forward or late.
The correction value .increment.t is counted by a .increment.t counter 35. On the other hand, at the rising edge of the forward/late signal 47a/b, a count value indicating a time passage T of a T1 counter 32, which is counting hour pulses from a preceding correction, is registered in a T register 34, and at the falling edge of the forward/late signal 47a/b, the T1 counter 32 is reset for counting hour pulses until a next correction.
The time passage T is divided by the correction value .increment.t by a divider 36 and registered in a T/.increment.t register 37 as a correction interval T/.increment.t.
A comparator 38 generates a correction signal 46 each time a count value of a T2 counter 33, which is also counting the hour pulses and reset by the correction signal 46, attains the correction interval T/.increment.t. With the correction signal 46, the correction circuit 39 suppresses or adds a one second pulse referring to the polarity registered in the polarity register 40.
Thus, the lead or lag of time indication is corrected automatically in the prior art of FIG. 3.
In another Japanese patent application laid open as a Provisional Publication No. 9732/'84 (hereafter called the second prior art), a self-correcting timer provided in a computer and backed up with a battery is disclosed, wherein timer correction data registered in a non-volatile memory is revised every time a user corrects the timer indication through its key board. The self-correcting timer self-corrects the timer indication at a certain interval referring to the timer correction data.
In still another Japanese patent application laid open as a Provisional Publication No. 11384/'81 (hereafter called the third prior art), there is disclosed a computer equipped with a timer, wherein a correction value and a correction interval in a battery backed up RAM are set by a customer engineer, for example, together with last correction date. When the computer is raised up, the computer refers the last correction date, and if more than the correction interval is passed from the last correction date, the computer corrects the timer with the correction value, revising the last correction date by adding the correction interval thereto.
However, in the self-correction watch of the first prior art, there is a problem that the correction interval T/.increment.t is written over the previous correction interval, and so the user should manipulate the correction switch 31 considering the previous correction value for correcting the watch correctly after a second correction.
In the second prior art, the timer correction should be entered through the key board, and an appropriate correction value should be prepared in the third prior art, because, otherwise, incorrect correction is left repeated. These are also problems which are present in the prior art.